The present invention relates to torque limiting drives, or friction clutches as they are sometimes called, of the type permitting slippage at torques above a predetermined level or value. Drivers of this type find application in timing mechanisms and programmer/timers for appliances. Devices of this type, and particularly programmer/timers for appliances typically utilize a small, sub-fractional horsepower timing motor driving an advance mechanism for advancing a rotating cam which sequentially actuates various electrical switches for effecting the various functional operations for the appliance service cycle or program.
Where an appliance is controlled by a timing motor advancing a rotary cam for sequentially actuating a plurality of switches, it is common practice to arrange the rotary cam such that it can be turned manually by the appliance user to a desired position representing a portion of the program prior to energizing the timing motor for beginning the appliance program cycle. Such an arrangement requires that the cam drum be rotated or advanced by the user against the friction forces of the cam followers for all of the switches and against the forces of the timer advancing mechanism or require that the advancing mechanism be released to permit such cam rotation by the user.
Heretofore, user rotation for program selection by rotating the of the appliance programmer/timer has resulted in difficulty in designing the program cam advance mechanism and the cam followers for the switches to permit such rotation without undue torque being applied by the user or without causing damage to the advance mechanism in the event of reverse rotation of the cam. Thus, it has been desired to provide a way or means of permitting the user to rotate the program cam of a timer motor advanced switching cam in an appliance programmer/timer without causing damage to the advance mechanism or presenting difficulties in the user manually applying the torque necessary to advance the cam against the friction forces of the switches.